According to the latest American Cancer Society's annual statistical report, released in January 2005, cancer has edged out heart disease as the leading cause of death in Americans under age 85. In 2002, the most recent year for which information is available, 476,009 Americans under 85 died of cancer compared with 450,637 who died of heart disease (those under 85 comprise 98.4 percent of the US population). Protein tyrosine kinases (PTK), which historically represented the majority of first discovered oncogenes, remain today one of the most important classes of oncology drug targets.
Protein kinases are enzymes which covalently modify proteins and peptides by the attachment of a phosphate group to one or more sites on the protein or peptide (for example, PTK phosphorylate tyrosine groups). The measurement of protein kinase activity is important since studies have shown that these enzymes are key regulators of many cell functions.
Over 500 protein kinases have been identified in the human genome (“kinome”) (Manning et al. (2002) Science. 298:1912). Based on the recent advances in deciphering the human genome, the family of human PTK consists of approximately 90 members (Blume-Jensen and Hunter (2001) Nature, 411: 355-365; Robinson et al. (2000) Oncogene 19:5548-5557). This family can be divided in two major groups—receptor tyrosine kinases (RTK) and cytoplasmic (or non-receptor) tyrosine kinases (CTK)—and approximately 30 subfamilies based on structural similarity (see, e.g., Bolen et al. (1992) FASEB J. 6:3403-3409 (1992); Ullrich and Schlessinger (1990) Cell 61:203-212; Ihle (1995) Sem. Immunol. 7:247-254. PTKs are involved in regulation of many cellular processes, such as cell proliferation, survival and apoptosis. Enhanced activity of PTKs has been implicated in a variety of malignant and nonmalignant proliferative diseases. In addition, PTKs play a central role in the regulation of cells of the immune system. PTK inhibitors can thus impact a wide variety of oncologic and immunologic disorders. Such disorders may be ameliorated by selective inhibition of a certain receptor or non-receptor PTK, such as LCK, or due to the homology among PTK classes, by inhibition of more than one PTK by an inhibitor.
In some forms of cancer, a PTK mutation or structural alteration can increase the ability to proliferate, and thus, provides an advantage over surrounding cells. PTK of growth factor receptors, for instance, have been shown to be involved in the transformation of normal to cancerous cells (see, e.g., Rao (1996) Curr. Opin. Oncol. 8:516-524). PTK also play a role in the regulation of apoptosis or programmed cell death (see, e.g., Anderson (1997) Microbiol. Rev. 61:33). By activation of PTK, apoptosis mechanisms can be shut off and the elimination of cancerous cells is prevented. Thus, PTK exert their oncogenic effects via a number of mechanisms such as driving proliferation and cell motility and invasion. These PTK include HER2, BCR-ABL, SRC, and IGF1R.
There are many ways that a PTK can become oncogenic. For example, mutations (such as gain-of-function mutations) or small deletions in RTK and/or CTK are known to be associated with several malignancies (e.g., KIT/SCFR, EGFR/ERBB1, CSF-1R, FGFR1, FGFR3, HGFR, RET). Additionally, overexpression of certain types of PTK resulting, for example, from gene amplification has been shown to be associated with several common cancers in humans (e.g., EGFR/ERBB1, ERBB2/HER2/NEU, ERBB3/HER3, ERBB4/HER4, CSF-1R, PDGFR, FLK2/FLT3, FLT4/VEGFR3, FGFR1, FGFR2/K-SAM, FGFR4, HGFR, RON, EPHA2, PEHB2, EPHB4, AXL, TIE/TIE1). For a review of oncogenic kinase signaling, and mutated kinase genes that may be used in the systems and methods provided herein, see Blume-Jensen and Hunter (2001) Nature 411:355; Tibes et al (2005) Annu. Rev. Pharmacol. Toxicol. 45:357; Gschwind (2004) Nature Reviews 4:361; Paul and Mukhopadhay (2004) Int. J. Med. Sci (2004) 1:101;
The majority of PTKs are believed to be important drug targets, especially for anti-cancer therapy. Indeed, a very large proportion of known PTKs have been shown to be hyperactivated in cancer cells due to overexpression or constitutively activating mutations and to directly drive tumor growth. In addition, a subset of RTKs, such as vascular endothelial growth factor receptors (VEGFR), fibroblast growth factor receptors (FGFR) and some ephrin receptor (EPH) family members, is involved in driving angiogenesis while others (e.g., Met and discoidin domain receptor (DDR)) promote cell motility and invasion (e.g., metastasis).
The formation of new blood vessels, either from differentiating endothelial cells during embryonic development (vasculogenesis) or from pre-existing vessels during adult life (angiogenesis), is an essential feature of organ development, reproduction, and wound healing in higher organisms. Folkman and Shing, J. Biol. Chem., 267: 10931-10934 (1992); Reynolds et al., FASEB J., 6: 886-892 (1992); Risau et al., Development, 102: 47′-478 (1988). Angiogenesis is implicated in the pathogenesis of a variety of disorders, including, but not limited to, solid tumors, intraocular neovascular syndromes such as proliferative retinopathies or age-related macular degeneration (AMD), rheumatoid arthritis, and psoriasis (Folkman et al., J. Biol. Chem. 267:10931-10934 (1992); Klagsbrun et al., Annu. Rev. Physiol. 53:217-239 (1991); and Garner A, “Vascular Diseases”. In: Pathobiology of ocular disease. A dynamic approach. Garner A, Klintworth G K, Eds. 2nd Edition Marcel Dekker, NY, pp 1625-1710 (1994)). For example, vascularization allows tumor cells in solid tumors to acquire a growth advantage and proliferative freedom as compared to normal cells. Accordingly, a correlation has been observed between microvessel density in tumors and patient survival with various cancers and tumors (Weidner et al., N Engl J Med 324:1-6 (1991); Horak et al., Lancet 340:1120-1124 (1992); and Macchiarini et al., Lancet 340:145-146 (1992)).
A number of RTK have been identified that govern discrete stages of vascular development (Folkman et al., Cell, 87:1153-1155 (1996); Hanahan, D., Science, 277:48-50 (1997); Risau, W., Nature, 386:671-674 (1997); Yancopoulos et al., Cell, 93:661-664 (1998)). For example, VEGFR2 (FLK1), a receptor for vascular endothelial growth factor (VEGF), mediates endothelial and hematopoietic precursor cell differentiation (Shalaby et al., Nature, 376:62-66 (1995); Carrneliet et al., Nature, 380:435-439 (1996); Ferrara et al., Nature 380:439-442 (1996)). VEGF also governs later stages of angiogenesis through ligation of VEGFR1 (FLT1) (Fong et al., Nature, 376:66-70 (1995)). Mice that lack VEGFR1 have disorganized vascular endothelium with ectopic occurrence of endothelial cells from the earliest stages of vascular development, suggesting that VEGFR1 signaling is essential for the proper assembly of endothelial sheets (Fong et al., supra). Another tyrosine kinase receptor, TEK (TIE2) (Dumont et al., Genes Dev. 8:1897-1909 (1994); Sato et al., Nature, 376:70-74 (1995)) and its ligands ANG1 (Davis et al., Cell 87:1161-1169 (1996); Suri et al., Cell 87:1171-1180 (1996)) and ANG2 (Maisonpierre et al., Science 277:55-60 (1997)) are involved in assembly of non-endothelial vessel wall components. TIE (TIE1) is involved in maintaining endothelial integrity, and its inactivation results in perinatal lethality due to edema and hemorrhage (Sato, et al., Nature 376:70-74 (1995)). The TEK pathway seems to be involved in maturation steps and promotes interactions between the endothelium and surrounding vessel wall components (Suri et al., supra; and Vikkula et al., Cell 87:1181-1190 (1996)).
The EPH tyrosine kinase subfamily appears to be the largest subfamily of transmembrane RTK (Pasquale et al., Curr. Opin. Cell Biol. 9:608-615 (1997); and Orioli and Klein, Trends in Genetics 13:354-359 (1997)). Ephrins and their EPH receptors govern proper cell migration and positioning during neural development, presumably through modulating intercellular repulsion (Pasquale, supra; Orioli and Klein, supra). Bidirectional signaling has been observed for some Ephrin-B/EPHB ligand/receptor pairs (Holland et al., Nature 383:722-725 (1996); and Bruckner et al., Science 275:1640-1643 (1997)). For example, Ephrin-A1 and Ephrin-B1 have been-proposed to have angiogenic properties (Pandey et al., Science 268:567-569 (1995); and Stein et al., Genes Dev. 12:667-678 (1998)). Ephrin-B2, a ligand for EPHB4 receptor, was recently reported to mark the arterial compartment during early angiogenesis, and mice that lack Ephrin-B2 showed severe anomalies in capillary bed formation (Wang et al., Cell 93: 741-753 (1998)).
Thus, blocking tyrosine kinase activity represents a rational, targeted approach to cancer therapy. Additionally, because tyrosine kinases have a number of other diverse biological functions, such as regulation of metabolism, cell differentiation, inflammation, immune responses, and tissue morphogenesis, kinases are attractive for drug development outside oncology.